Making Artificial Limbs More Comfortable

During the decade-long civil war in Sierra Leone, rebels would cut off the arms and legs of civilians as a scare tactic, leaving behind thousands of war amputees. After the war, 2015 National Geographic Emerging Explorer David Moinina Sengeh, who was born and raised in Sierra Leone, became involved in helping these amputees. They were given prosthetics to wear, but most chose not to wear them because they were so uncomfortable.

Later in life, Sengeh joined the Biomechatronics group in the MIT Media Lab as a Ph.D. candidate, where he began work on designing comfortable prosthetics. There, he began to realize that it wasn't just the prosthetics in Sierra Leone that were uncomfortable.

The National Geographic Live series brings thought-provoking presentations by today’s leading explorers, scientists, photographers, and performing artists right to you. Each presentation is filmed in front of a live audience at National Geographic headquarters in Washington, D.C.

Sengeh: Hundred percent of people living with amputations experience prosthetic socket discomfort. It's both a technology problem and it's a science problem because we don't really know how to connect the body to machines.

There are ten million people living with amputations globally. They could have gotten those from accidents victims of war or diabetes. They range from people who are in the US to people who are in my home in Sierra Leone to Cambodia, all over the world. But one thing is constant. Hundred percent of them experience prosthetic socket discomfort.

That's a residual limb with bones inside. That is very different for everybody. The part that connects that residual limb to the prosthetic leg is uncomfortable. And part of that is because the way we conventionally make prosthetic sockets today is through an artisanal process for an ever changing human body that is so diverse across the population and across the whole world. And the way prosthesis prosthetic sockets are designed today is you go to a prosthetist and they take your leg and they squeeze your leg and ask you, “How does that feel if I press here a little bit does it feel great? What about that, what about your patellar tendon? What about this bone that's there is there a bone in there I don't know? How did this happen?” You get the picture. It is not repeatable. It is based on the experience of the prosthetist. And the mold that is created is based on somebody's experience. You create and alter that positive mold you make a negative mold and then you pour another positive mold inside and then you modify that, and then you make a test socket and then the person goes into the test socket they give you feedback, like telling “Oh, I don't think it's comfortable here” and then you modify it again and then you do this over and over and again. Until you or the person goes “Yeah, it's fine, I can work in this.”

And when you do get carbon fiber sockets of single material you have your residuum get blisters and pressure sores. If you look closely around the fibular head there you can see some blood spots. It's both a technology problem and it's a science problem because we don't really know how to connect the body to machines. So, one of the things that I was interested in with my boss was how do you understand the science behind designing for comfort. So, on the left is a fit-socket, which is an array of indentors in which the person inserts their residuum to capture experimental data of force, displacement and time so we can use it to characterize the model of the person's body. I decided that it was perhaps useful to link those points with a MRI, so that we can create models and we can link the experimental data to the modeling data directly. So, we have these markers that you can see in an MRI and you segment that MRI, so we define the bones define the skin, define all the other soft tissue. And then we can create in an exact replica, so we can ask questions around design of the interfaces we have. And then we can build models that is predictive, and we can use these to now say what happens inside the body. How is the soft tissue straining around the bone. We can test all of these now and go in and say “Well, we don't need to make a single material socket anymore. We can now take your body with all those markers that we put and that model that we created that was validated and that's predictive create an element all across your body with which we create the sockets where each color is a new material and test this hypothesis.”

Why does this all matter? Why... why does understanding the science of how we connect the body to machines matter? Your shoes still give you blisters. If you know somebody who has scoliosis they hate wearing their brace. If you have a knee or an ankle injury, you hate your braces. And that's because we don't know how to connect the body comfortably to machines. And, the science behind designing for comfort really starts from being able to merge these experimental and numerical data and build predictive models, and ask questions around how our design actually affects the behavior of the body as we use these machines in time and across loads and across different terrains.

Making Artificial Limbs More Comfortable

During the decade-long civil war in Sierra Leone, rebels would cut off the arms and legs of civilians as a scare tactic, leaving behind thousands of war amputees. After the war, 2015 National Geographic Emerging Explorer David Moinina Sengeh, who was born and raised in Sierra Leone, became involved in helping these amputees. They were given prosthetics to wear, but most chose not to wear them because they were so uncomfortable.

Later in life, Sengeh joined the Biomechatronics group in the MIT Media Lab as a Ph.D. candidate, where he began work on designing comfortable prosthetics. There, he began to realize that it wasn't just the prosthetics in Sierra Leone that were uncomfortable.

The National Geographic Live series brings thought-provoking presentations by today’s leading explorers, scientists, photographers, and performing artists right to you. Each presentation is filmed in front of a live audience at National Geographic headquarters in Washington, D.C.